Generally, a rotor such as an armature, which rotates about an axis, can be avoided from vibrating during its rotation only under the condition in which the mass of the rotor is uniformly distributed around the axis. In such a rotor, however, there is weight unbalance, that is, an unbalanced portion, with respect to the axis of the rotor due to various reasons such as machining errors, and unbalanced molecular arrangement.
Since such an unbalanced portion causes the rotor to vibrate, it is necessary to make the center of weight of the rotor coincide with the axis of the rotor by appropriately eliminating the unbalance amount of the unbalanced portion, that is, appropriately increasing or reducing the weight of the unbalanced portion. In this connection, balancing machines have been proposed. Balancing machine is an apparatus for detecting the unbalance position and unbalance amount of a rotor, and correcting the unbalance of the rotor based on the detected result, thereby making the center of weight of the rotor coincide with the axis of the rotor. Such a balancing machine operates in an additive correction fashion or in a subtractive correction fashion in accordance with an unbalance correction method used therein. In accordance with the additive correction fashion, a desired balance is obtained by adding a weight to a smaller mass portion. In accordance with the subtractive correction fashion, a desired balance is obtained by cutting a desired amount from a lager mass-portion.
The configuration of a balancing machine operating to perform a subtractive unbalance correction will now be described in conjunction with an armature with reference to FIGS. 1a to 2b. 
FIGS. 1a and 1b are perspective views respectively illustrating general armatures. FIG. 2a is a plan view illustrating a conventional 6-axis armature balancing machine. FIG. 2b is a plan view illustrating a conventional 2-axis armature balancing machine. In FIGS. 1a to 2b, identical elements are denoted by the same reference numeral in order to avoid a repeated description thereof.
First, the configuration of the general armature will be described with reference to FIGS. 1a and 1b. The armature, which is denoted by the reference numeral 1, includes a shaft 2, a laminated core 3 fixedly mounted around the shaft 2, wire coils 5 wound along slots 4 formed at the core 3, and a commutator 6 mounted to the shaft 2 near one end of the shaft 2. When the armature 1, which is the rotor of a motor, is unbalanced about its rotating axis in terms of weight, it may vibrate during its rotation.
For this reason, the balance accuracy of the armature 1 has a close relation with the performance of the motor using the armature 1 as its rotor. Since recent industrial developments cause an increased demand for motors having a superior performance, more accurate armatures having a higher balance accuracy have been required.
Now, the configuration of the conventional 6-axis armature balancing machine for measuring the balance of the above described armature, and machining the armature based on the measured result, will be described with reference to FIG. 2a. As shown in FIG. 2a, the 6-axis armature balancing machine includes a lift unit L for supplying the armature 1 to be subjected to a measuring process, and discharging the measured armature 1 to be subjected to a machining process, and a first balance measuring unit B1 for measuring unbalance amounts and positions of the armature 1 at opposite axial portions, that is, left and right axial portions, of the core 3 in the armature 1, respectively. The armature balancing machine also includes a first cutting unit C1 for removing the unbalance amount of the armature 1 measured by the first balance measuring unit B1 at the left portion of the core 3, in accordance with a cutting process using a cutting tool, a rotating unit R for rotating the armature 1 to position the right unbalanced portion of the armature 1 at a cutting point, and a second balance measuring unit B2 for re-measuring a possible unbalance amount of the armature 1 subjected to the cutting process at its left and right unbalanced portions. The armature balancing machine further includes an index device I for feeding the armature 1 to each of the units L, B1, C1, R, C2, and B2 while being vertically movable, and a control unit (not shown) for detecting the unbalance amounts and positions of the armature 1 based on signals outputted from the balance measuring units B1 and B2, and outputting operation control signals, generated based on the detected results, to the remaining units L, C1, R, and C2, thereby compensating for the unbalance of the armature 1. The index device I includes: a plurality of index arms having the same number as that of the above described units, and a finger unit 20.
Each of the balance measuring units B1 and B2 includes a servo motor or stepping motor having a pulley to which the armature 1 is connected via a belt, and a balance measuring section arranged near the armature 1 to measure the unbalance amount and position of the armature 1. The control unit rotates the armature 1 at a predetermined RPM by outputting pulses to the drive motor, based on a vibration signal generated through a vibration measuring sensor alone or together with a reference point sensor. During the rotation of the armature 1, the control unit detects the position (angle) and unbalance amount of each unbalanced portion in the armature 1 through a calculation circuit and a calculation program. The calculation circuit and program may be of various types, for example, an AIFA WATT METRIC type, a FILT type, an FFT type, a WATT METRIC type, or a synchronous rectification type.
The control unit also generates operation control signals based on signals outputted from the balance measuring units B1 and B2, and outputs those operation control signals to the lift unit L, cutting units C1 and C2, and rotating unit R, respectively. Under the control of the control unit, respective unbalanced portions of the armature 1 are positioned at cutting points of cutting tools included in the cutting units C1 and C2 by the index device I. When the armature 1 is fed to the first cutting unit C1 or the second cutting unit C2 by the index device I, its unbalanced portion is cut by the associated cutting unit in accordance with a cut depth and axial cutting length determined by a predetermined unbalance amount.
The configuration of the conventional 2-axis armature balancing machine will be described with reference to FIG. 2b. As shown in FIG. 2b, the 2-axis armature balancing machine includes a balance measuring unit B3 for measuring respective unbalance amounts and positions of the armature 1 at opposite axial portions, that is, left and right axial portions, of the core 2 in the armature 1 fed by a conveyor belt, a cutting unit C3 for cutting the armature 1, based on each unbalance amount measured by the balance measuring unit B3, and a rotating unit R3 for rotating the armature 1, based on each unbalance position measured by the balance measuring unit B3. The 2-axis armature balancing machine also includes an index device I3 for feeding the armature 1 completing its unbalance test from the balance measuring unit B3 to the cutting unit C3, upwardly moving, rotating 180°, and then downwardly moving the cutting unit C3 on the cutting unit C3 for cutting the left and right portions of the armature 1, and feeding again the corrected armature 1 from the cutting unit C3 to the balance measuring unit B3. The 2-axis armature balancing machine further includes a control unit for outputting operation control signals to the rotating unit R3, cutting unit C3, and index device I3 in order to achieve an unbalance correction based on the signal outputted from the balance measuring unit B3. In the 2-axis armature balancing machine, the armature 1, which has vertically moved by the index device I3, may be 180° rotated without being downwardly moved. That is, the armature 1 can be rotated at a fixed position by the rotating unit R3.
The cutting amount in the cutting process is determined by the upward movement length of a blade included in the cutting tool, and the axial forward and backward movement length of the blade. The upward movement length of the blade, that is, the cutting depth, and the axial forward and backward movement length, that is, the axial cutting length, are set based on the unbalance amount of the armature by the user. Examples of this setting are illustrated in FIG. 3.
FIG. 3 shows graphs depicting an unbalance correction amount varying depending on the unbalance amount. As indicated by the graph denoted by the reference numeral “1”, the cutting depth and axial cutting length are set based on each of sampled unbalance amounts. For example, the unbalance correction amount may be 0.1 mm for an unbalance amount of 50 mg, and 0.2 mm for an unbalance amount of 100 mg. When a measured unbalance amount is determined to be within a range between the set unbalance amounts, the associated cutting depth and axial cutting length are determined by proportionally estimating them based on the set values.
FIGS. 2a to 3 illustrate an example in which a subtractive unbalance correction is carried out. In the case of an additive unbalance correction, the balancing machine automatically discharges a weight determined based on the predetermined unbalance amount, and attaches the discharged weight to the rotor at its unbalance position. In order to discharge a desired weight amount, discharge time and pressure are adjusted.
Although the unbalance correction by the balancing machine has been described as being applied to armatures, it may be applicable to any objects requiring balance correction. Since these objects may be appreciated by those skilled in the art, no detailed description thereof will be given.
However, the above described balancing machine may involve errors in unbalance correction position and amount due to an erroneous setting of the cutting tool, a linear or non-linear abrasion of the blade edge in the cutting tool occurring during its use due to an erroneous setting of the cutting tool, an angular error generated during the rotation of the index device, vertical and axial mechanical tolerances occurring during the vertical and axial movements of the index device, a mechanical tolerance caused by a temperature difference, an erroneous measurement of unbalance angle and amount occurring due to a variation in measurement condition caused by an abrasion of the belt or drive pulley, or erroneous unbalance correction position and amount caused by various errors generated due to a variation in the temperature characteristics of various electronic elements included in the control unit. Examples of such errors will now be described with reference to FIGS. 3 to 5d. 
Although an unbalance amount and an unbalance correction amount according to the unbalance amount should be linearly proportional to each other, as indicated by the graph 1 of FIG. 3, their practical relation is non-linear, as indicated by graphs 2 and 3 in FIG. 3. Such a non-linearity results from the above described causes of various unbalance correction errors.
As described above, unbalance correction errors may be generated due to an erroneous setting of the cutting tool. For example, the cutting tool should be set in such a fashion that the blade edge 9 and the armature 1 are concentric, as shown in a part “a” of FIG. 4. However, where the blade edge 9 and the armature 1 are eccentric, as shown in a part “b” or “c” of FIG. 4, that is, an erroneous setting of the cutting tool occurs, the unbalance correction is not achieved at a correct position, as indicated by black portions in the parts “a” to “c” of FIG. 4.
Where there is no error in association with the unbalance correction position, as shown in the part “a” of FIG. 4, the corrected position is at 0° or 180° under the condition in which the initial unbalance position is 0° (FIG. 5a), as shown in FIG. 5b. In the case of the armature having an unbalance at a position indicated by a black circle in the part “A-1” of FIG. 5b, its unbalance correction is accurately made at a position of 0°. When the unbalance correction amount is less than the unbalance amount in the case shown in the part “A-1” of FIG. 5b, there is an unbalance amount remaining at the position of 0° after the unbalance correction, as shown in the part “A-2” of FIG. 5b. On the other hand, when the unbalance correction amount is more than the unbalance amount, there is an unbalance amount remaining at a position opposite to the initial unbalance position after the unbalance correction, as shown in the part “A-3” of FIG. 5b. In this case, the initial unbalance position is shifted by an angle of 180°. In either case, the unbalance correction amount should be adjusted because although the unbalance correction position is correct, there is an error in the unbalance correction amount.
Where there is an error in unbalance position (angle) due to various factors including the erroneous setting as shown in the part “b” or “c” of FIG. 4, the unbalance correction is carried out at an incorrect position, as shown in FIG. 5c or 5d. This will be described in detail hereinafter.
Results shown in FIG. 5c are generated when there is an error in unbalance correction position, and the correction amount is less than the unbalance amount. Although the initial unbalance position is the position of 0°, as shown in FIG. 5a, an angular error may occur due to a composite reason, as shown in the part “B-1” or “C-1” of FIG. 5c. In this case, the unbalance correction is carried out in accordance with a correction angle and correction amount vector-calculated based on the measured unbalance amount and the erroneous angle as shown in the part “B-1” or “C-1” of FIG. 5c. In the cases respectively shown in the parts “B-1” to “B-3” and “C-1” to “C-3” of FIG. 5c, their angular errors (angular deviations) have relations of “B-1<B-2<B-3” and “C-1<C-2<C-3” with respect to 0°. That is, the case “B-2” has an angular deviation toward 270° larger than that of the case “B-1”, and the case “B-3” has an angular deviation toward 270° larger than that of the case “B-2”. On the other hand, the case “C-2” has an angular deviation toward 90° larger than that of the case “C-1”, and the case “IC-3” has an angular deviation toward 90° larger than that of the case “C-2”.
Results shown in FIG. 5d are generated when there is an error in unbalance correction position, and the correction amount is more than the unbalance amount. Although the initial unbalance position is the position of 0°, as shown in FIG. 5a, an angular error may occur due to a composite reason, as shown in the part “D-1” or “E-1” of FIG. 5d. In this case, the unbalance correction is carried out in accordance with a correction angle and correction amount vector-calculated based on the measured unbalance amount and the erroneous angle as shown in the part “D-1” or “E-1” of FIG. 5d. In the cases respectively shown in the parts “D-1” to “D-3” and “E-1” to “E-3” of FIG. 5d, their angular errors (angular deviations) have relations of “D-1<D-2<D-3” and “E-1<E-2<E-3” with respect to 0°. That is, the case “ID-2” has an angular deviation toward 270° larger than that of the case “D-1”, and the case “D-3” has an angular deviation toward 270° larger than that of the case “D-2”. On the other hand, the case “D-2” has an angular deviation toward 90° larger than that of the case “D-1”, and the case “D-3” has an angular deviation toward 90° larger than that of the case “D-2”.
When the unbalance compensation is inaccurately achieved, as mentioned above, there is a problem in that the probability that the rotor emerging from the balancing machine has a good quality is reduced to 60% or less. Once the primary unbalance correction is made at a certain position, it is impossible to carry out a re-correction at the same position. For this reason, there is a large defective proportion of products. In the case of an additive unbalance correction, there is a problem in that the weight attached to the rotor may be separated from the rotor during the operation of the rotor. Furthermore, there is waste of resources because most of rotors determined to have a poor quality must be disposed of.
In order to reduce the defective proportion of products, a new setting of the balancing machine may be carried out under the condition in which the balancing machine is stopped, in accordance with conventional techniques. Conventionally, the setting of the balancing machine is carried out periodically or whenever it is determined that the rate of products having a poor quality is too high. The adjustment of the cutting depth and axial movement distance of the cutter associated with the setting of the balancing machine is determined only based on the immediate perception of the operator. For this reason, there is a limitation in reducing the rate of products having a poor quality. Moreover, the quality of products is limited. Also, there is a degradation in productivity.